This application claims priority on Finnish Application No. 20010721, filed Apr. 6, 2001, the disclosure of which is incorporated by reference herein.
Not applicable.
The present invention relates to the manufacture of paper, board and pulp and in particular, and to presses of their wire, pre-press and press sections. In certain application, an abundance of open water space is needed in connection with a press nip in the press section in order that the water removed from a web during pressing may be passed out of connection with the web and the press nip.
In the prior art, roll covers are known in which various groove patterns are used. With respect to the prior art relating to these, reference may be made to laid-open publications DE 196 31 404 and DE 196 31 405. These publications describe some arrangements with a roll cover provided with groove patterning.
In the prior art, press roll belts are also known in which the belts are made of crosswise woven threads, but they do not provide a large open water volume because the surface that is formed is smooth. One such arrangement is disclosed in EP publication 0 889 164.
With respect to the prior art, reference is also made to EP patent 0 336 876 disclosing an extended-nip press belt which is provided with grooves extending in the running direction of the web.
As known in the prior art, a press concept comprises at least one press nip formed between two rolls, one of which can be, for example, a shoe press roll. The web runs through the press nip while supported by a fabric, and water is removed from the web by pressing in the press nip. In paper, board and pulp machines there are press nips in the press section as well as in the wire section and the pre-press section as press units. In one prior art application, the press concept of the wire section comprises a roll press and a shoe press in which the same press felt and the same wet wire are passed through both nips.
As known in the prior art, in some applications, the belt of a shoe press roll can be provided with a water volume of about 250-500 g/m2 by means of grooves and with a water volume of up to about 600 g/m2 by means of grooves and blind-drilled bores. One problem with these prior-art grooved belts is that, when the belt becomes older, the raised portions between the grooves break and, based on experience, a narrower and higher raised portion, i.e. the portion between the grooves, breaks more easily than a lower and broader portion. The belt can also be manufactured so that it is grooved and blind-drilled bored, which is somewhat more durable than a merely grooved belt, but this option is not applicable when high water handling capacity is needed because, during the pressing process, less water is guided into a blind-drilled surface than into a grooved one, even though the water volume would be the same, because no flow of water is produced in the holes of a blind-drilled surface, unlike the grooves of a grooved surface where a flow of water is produced.
An object of the invention is to provide a press roll belt which has a large water volume and thus also high water handling capacity. In addition, its durability is superior to that of prior-art designs.
A further object of the invention is also to provide a press roll belt which has high water handling capacity and which does not mark the surface of the web.
An object of the invention is also to provide press concepts in which water handling capacity is high.
In accordance with the invention, a groove pattern is used in a press roll belt either in a belt in connection with a roll or in a separate belt arranged in connection with a roll, which groove pattern is formed of intersecting grooves producing a quadrangle pattern, for example, a rhombus pattern, a rectangle pattern, a parallelogram pattern, a square pattern, a diamond pattern. The water volume of the belt is increased by this kind of groove pattern, however, without losing surface strength properties. The angle between the intersecting grooves in the direction of rotation of the roll is 40-140xc2x0, preferably 70-100xc2x0. When better durability is needed, a smaller angle is selected, preferably about 70xc2x0. In accordance with an advantageous feature of the invention, two groove patterns are formed of intersecting grooves, one of the patterns being placed between the grooves of the other pattern, which groove patterns have different groove depths.
In this description, the term xe2x80x9cpress roll beltxe2x80x9d means both a belt arranged in connection with a roll, i.e. a belt forming an integral part of the roll, and a separate belt arranged in connection with a roll, which belt has its own belt loop and rolls associated therewith, unless it clearly appears otherwise from the context.
In accordance with the invention, a surface pattern having a large water volume is achieved by this means, said pattern having a durable structure and allowing the open surface area/water volume to be changed in a wider area than allowed by the machine-direction grooves used in prior-art applications. The groove pattern in accordance with the invention is also simple to manufacture.
By means of the patterning in accordance with the invention, for example, the following values are achieved with different width and depth values of the groove: groove width may be, for example, 0.5-1.5 mm and groove depth 0.5-1.0 mm, the open surface area 25-60%, in which case the water volume is, for example, with groove depth 1.0 mm, groove width 1 mm, open surface area 31%, piece size 5xc3x975 mmxe2x86x92water volume of 305 g/m2; with groove depth 1.0 mm, groove width 1 mm, open surface area 49%, piece size 2.5xc3x972.5 mmxe2x86x92water volume of 490 g/m2; with groove depth 1.5 mm, groove width 1.5 mm, open surface area 61%, piece size 2.5xc3x972.5 mmxe2x86x92water volume of 914 g/m2, and with groove depth 1.6 mmxe2x86x92water volume of 1000 g/m2.
In the press concept in accordance with the invention, at least one press nip is formed such that at least one roll forming a press nip with another roll has a cover or a roll belt or a separate belt used in connection with the roll which is provided with groove patterning, quadrangle patterning, formed of intersecting grooves, whereby the water volume can be increased in the press nip. The press concept in accordance with the invention is suitable for use in the manufacture of paper, board and pulp in connection with press nips of a wire section, pre-presses and a press section.
In accordance with an advantageous embodiment example of the invention, when two groove patterns of different depth are used in the quadrangle patterning, the xe2x80x9cpartial piecesxe2x80x9d defined by the grooves do not come off, which improves the durability of the belt used in the press concept, in particular when water volume is large. Thereby is also provided a larger water volume and a more durable structure as compared with grooves of equal depth.
In the press concepts in accordance with the invention, a belt provided with a groove pattern is advantageously used in connection with an extended nip roll, in particular on a roll on the wire side and in press roll belts.
One application in accordance with the invention is an extended nip press in which one of the rolls has a groove pattern in accordance with the invention either in a separate belt arranged in connection with a lower roll or in the belt or cover of a counter roll.
The invention is applied in web dewatering presses, in particular in connection with the manufacture of paper, board and pulp webs.
The press concept in accordance with the invention can be applied, for example, in presses of a wire section in a pulp machine, in which connection the water quantities to be removed are as follows: a roll press about 500-700 g/m2 and a shoe press about 1000-1300 g/m2. These large water quantities to be removed also require a large water space in the surface of counter rolls, and large water volumes are achieved by the concepts in accordance with the invention. A large water volume is provided by means of intersecting grooves, for example, by grooves which intersect at an angle of 90xc2x0 and which provide a quadrangle pattern. The press must handle large water quantities also when the solids entering the nip are low, for example, 10-14% with a basis weight of 80 g/m2 or 10% with a basis weight of 40 g/m2.